The Winter Icing and Storms Project (WISP) was conducted in the Colorado Front range area from February 1 - March 31 1990 (WISP90), January 15 - April 5 1991 (WISP91), February 15 - March 15 1993 (WISP93), and January 25 - March 25 1994 (WISP94). The main goals of the project are to: 1) ... study the processes leading to the formation and depletion of supercooled liquid water (SLW) in winter storms; and 2) improve forecasts of aircraft icing. During the WISP90 and WISP91 field seasons, 2 research aircraft, 4 Doppler radars, 49 Mesonet stations, 7 CLASS sounding systems, 3 microwave radiometers, and a number of other facilities were deployed in the Front Range area. A comprehensive dataset was obtained on 8 anticyclonic storms, 16 cyclonic storms, and 9 frontal passages. Thirty-six scientists representing the National Center for Atmospheric Research (NCAR), National Oceanic and Atmospheric Administration (NOAA) Environmental Research Laboratory (ERL), University of Wyoming, University of North Dakota, and the Colorado State University participated in the field program.

In 1988, the Federal Aviation Administration (FAA) funded the NCAR Research Applications Program (RAP) to plan a multiyear program to improve aircraft icing forecasting. Through a series of meetings with investigators interested in icing and other winter storm problems, a comprehensive research plan was formulated that included field research, forecasting exercises, and products and displays concerning testing and evaluation. The FAA Icing Forecasting Improvement Program Experimental Design (Politovich 1989) was completed in Fall 1989, afterwhich the 6-year program began. As the program evolved, it became clear that excellent opportunities existed for collaboration between investigators interested in aircraft icing, and those interested in understanding the physical processes active in Front Range winter storms. It was decided to form a larger research program that would encompass these broader interests, hence, WISP. The investigators agreed that the central unifying objective for WISP should be a better understanding of the processes responsible for the production and depletion of SLW, which is of primary concern to both research and operational communities.

In addressing the objectives, SLW formation/depletion and aircraft icing, WISP studied two main areas. The first, Storm Dynamics, considered anticyclonic storms, cyclonic storms, local topographic forcing, conditional symmetric instability, cold-air damming/barrier jets, synoptic and mesoscale fronts, and diabatic processes. The second area, Cloud Microphysics, focused on the formation of ice crystals, depletion of SLW, and production of large drops.

An array of instruments were used in WISP90 and WISP91. Two research aircraft, the University of Wyoming King Air and the University of North Dakota (UND) Citation II carried several instruments taking cloud physics, thermodynamics, and air-motion measurements. WISP90 utilized the NCAR CP-4 C-band and S-band Mile High Radar, while the Colorado State University (CSU) CHILL S-band, the UND C-band, and the NCAR CP-2 radar operated during WISP91, measuring reflectivity and Doppler velocity. The NOAA Wave Propagation Laboratory (WPL) operated 3 ground-based vertically pointing microwave radiometers sensitive to water vapor, precipitable (total path) water vapor, liquid water, and integrated liquid water. Wind-profiling radars provided vertical profiles of horizontal wind velocity. Using the Radio Acoustic Sounding System (RASS) (Westwater and Kropfli 1989), the radars also measured profiles of virtual temperature with the same resolution as the wind profiles. The new-generation National Weather Service (NWS) laser ceilometer obtained cloud-base height measurements. Zenith-viewing infrared radiometers were operated for WISP90 for cloud identification and during WISP91 for quantitative measurement of cloud-base temperature. Portable Automated Mesonet (PAM II) and Program for Regional Observing and Forecasting Systems (PROFS) surface weather stations reported temperature, dew point, pressure, humidity, wind speed and direction, peak wind, rainfall, snowfall, and global sky radiation. NCAR Cross-chain LORAN Atmospheric Sounding System (CLASS) stations were deployed retrieving pressure, temperature, dew point, and wind speed and direction. A network of voluntary snowfall observers in the field collected snow accumulation, snowfall rate, liquid equivalent, crystal habit, degree of riming, aggregate formation and size, wind speed and direction, snow start/end times, rainfall, and lightning.

Research using the WISP90 and WISP91 data is currently ongoing. The Valentine's Day storm during WISP90 characterized by the invasion of a polar air mass, overrun by southwesterly to southerly flow aloft represented an anticyclonic upslope storm. Heavy snowfall of 40-80 inch depth fell along the Front range from Cheyenne, Wyoming, to Denver, during the deep, cyclonic storm of March 6-7 1990. SLW droplets with diameters greater than 50 um were observed. A shallow cold front 3.5 km MSL caused temperatures to drop more than 10 degrees in a six-hour period January 19 1991. Ice crystal formation and evolution associated with a well-defined shallow upslope cloud developed during the Valentine's Day storm of 1990 as seen from the University of Wyoming King Air aircraft. During the two years of WISP field-data collection, a persistent problem encountered in formulating local nowcasts and forecasts was frequent mediocre and occasionally poor performance of NMC-based models such as the Nested Grid Model (NGM). This was clear March 29-30 1991 where significant snowfall was predicted by both the NGM and the Limited Fine-Mesh (LFM) models associated with an amplifying short wave approaching from the northwest.

The WISP93 experiment was an instrument testing (IT) project called WISP-IT. New instrumentation was tested to be used in the WISP94 experiment.

The WISP94 experiment featured 25 researchers from NCAR's Research Application Program, NOAA, and several universities searching for the secrets that cause supercooled water droplets and ice crystals to form in clouds. WISP94 focused on the origins of in-cloud ice. Air samples taken from just outside ice-bearing clouds are being rushed to a cloud chamber at Colorado State University where scientists are recreating the ice-production process that the air would have encountered within the cloud. This technique coupled with improved processing methods for ice-nucleus filter samples should yield a better understanding of nucleation mechanisms at work in winter storms.

The WISP team has identified shallow stratus decks as the source of the largest supercooled droplets, those with diameters from 50 to several hundred microns (0.002 to 0.01 inches). A number of innovative new instruments have sampled clouds from aboard the University of Wyoming's King Air and NCAR's Electra research aircraft. A U-band radar on the King Air operated jointly by the universities of Wyoming and Massachusetts will help resolve the fine-scale structure near cloud tops that may be responsible for generating the large droplets. Both aircraft flew to Kansas and Nebraska for very successful probes of extensive stratus decks. The King Air also studied intense snow and ice storms in Oklahoma